These days, I’ve been digging into Silverlight and going through a couple of websites and finding some materials, and I thought of sharing the same with you. There is nothing great I have done in this article except spend a couple of hours and compiled all the questions in one place.

In this article, you will learn the basics of the Silverlight technology.

Who should read this article?

This article is intended for everyone who wants to improve their skill set with Silverlight technology.

This article will be helpful if you are preparing for a Microsoft interview.

This article will be helpful if you are new to Silverlight and want to know more about it.

This article will be helpful if you are already familiar with Silverlight but looking for brush up knowledge.

This article will be helpful if you are looking for a quick tutorial on Silverlight technology.

This article will be helpful if you are looking for Frequently Asked Questions (FAQs) on Silverlight technology.

One of the design goals of the Silverlight technology is to fill the gap between Windows applications and Web applications in terms of creating Graphical User Interfaces (GUI).

Silverlight applications are run as client-side applications without the need to refresh the browser to update the UI. However, because of the built-in .NET framework, Silverlight applications can easily integrate with server-side controls and services. Using Silverlight's implementation of the .NET framework, developers can easily integrate existing libraries and code into Silverlight applications.

Silverlight integrates the XAML declarative language with the .NET framework.

It is a cross-browser, cross-platform technology which provides a consistent user experience everywhere it runs.

The Silverlight plug-in installs in seconds, and leaves a very small footprint.

After you install the plug-in, users no longer need to install anything on their workstations to run Silverlight applications. The applications are available to them from whatever browser they are accessing.

It runs a client-side application that can read data and update the UI without interrupting the user by refreshing the whole page.

It can run asynchronous communications with the server, allowing the UI to continue to function while waiting for the server response.

Mac OS

Linux

Moonlight is an Open Source implementation of Silverlight, primarily for Linux and other Unix/X11 based Operating Systems. In September of 2007, Microsoft and Novell announced a technical collaboration that includes access to Microsoft's test suites for Silverlight and the distribution of a Media Pack for Linux users that will contain licensed media codecs for video and audio.

Yes, Microsoft has made the Silverlight browser plug-in freely available for all supported platforms and browsers.

9. What is the difference between Silverlight 1.0 and 2?

Silverlight 1 is purely AJAX and JavaScript based. All the code has to be written in JavaScript and XAML.

Silverlight 2 supports managed code. When the Silverlight 2 runtime is installed, it installs a limited version of the .NET runtime on the client machine. This allows .NET programmers to write managed code to be executed on the client PC, and provides a better user experience to users. Of course, there is security restrictions built in to it so that the code has limited access to the client computer.

The biggest change is the implementation of the .NET Framework. If you are familiar with Silverlight 1.0, then you will be used to coding the application functionality in JavaScript. You can still implement functionality using JavaScript; however, you can now also implement functionality using C#, Visual Basic, Python, Ruby, and managed JavaScript.

Another major change is the introduction of the XAP package. In Silverlight 1.0, the XAML code was referenced directly by the Silverlight object embedded in the browser. In Silverlight 2, however, the embedded object references an XAP package that contains the XAP file, assemblies, and resources necessary to run the Silverlight application.

10. What is the Silverlight plug-in?

The Silverlight plug-in is a very lightweight component that is necessary for users to access Silverlight applications. The plug-in download and install takes only a few moments, and do not take up much hard drive space.

The Silverlight plug-in is responsible for accessing the Silverlight object in the Web page, downloading and accessing the XAP package, setting up the program environment, and beginning execution of the application.

When a Web page containing a Silverlight application is displayed, the user should be given a link to download the plug-in from Microsoft if the plug-in is not already installed.

Silverlight Runtime is a browser plug-in to support Silverlight enabled applications. If the Silverlight runtime is not installed, browsers will not be able to run Silverlight elements in the browser. You can set up your Silverlight tags in such a way that your browser will automatically prompt the user to download and install the Silverlight plug-in when your application is launched in the browser.

Installing the run time is a onetime operation on the client. Once installed, it will be automatically launched when any Silverlight application is loaded in the browser.

Note: Silverlight plug-in and the runtime, both are the same; however, I am giving two definitions here.

Silverlight SDK is a set of tools, documentation, samples, and templates for web developers to enable them to easily develop Silverlight enabled applications. The SDK is not really mandatory to develop Silverlight applications; however, the SDK will make development much easier.

Microsoft Expression Studio - This tool is meant for web designers to create rich visual elements for Silverlight applications. Expression Studio is recommended for web designers who create rich internet applications with enhanced visual content and graphics. There are several features provided for creating enhanced graphics elements, with lot of options to pick color, font, etc.

Download Silverlight Toolkit - This toolkit is a Microsoft project containing Silverlight controls, components, and utilities that can be downloaded and used in your Silverlight applications. It includes full source code, samples, and tests.

If your Silverlight application includes just graphics and visual elements, then you can use Expression Studio. However, if you are a programmer and if your Silverlight application includes programming logic, then you might want to choose Visual Studio.

Silverlight 2: Silverlight 2 (previously referred to as version 1.1) includes a version of the .NET Framework, implementing the same full Common Language Runtime (CLR) version as .NET Framework 3.0. The XAML markup as well as the code is compiled into .NET assemblies which are then compressed using Zip and stored in a .xap file.

Silverlight 3: Silverlight version 3 was released in July 9, 2009, which is an extension to Silverlight 2.0, and mainly provides improvements in graphics capabilities, media management, application development areas (additional controls, enhanced binding support, and out-of-browser functionality), and integration in the designers' Expression Blend 3 tools.

16. What is a .xap file?

A .xap file is a Silverlight-based application package (.xap) that is generated when the Silverlight project is built. A .xap file is the compressed output file for a Silverlight application. The .xap file includes AppManifest.xaml, the compiled output assembly of the Silverlight project (.dll), and the resource files referred to by the Silverlight application:

Web pages like .aspx files and .html files use Silverlight components by loading .xap files using the <object> tag in HTML or by using the <asp:Silverlight> tag in ASP.NET pages.

Rename this file to SilverlightTest.zip and open it using any decompression tool. You can see that this is just like any other zip file, and it includes the project's output DLL and another file called "AppManifest.xaml".

No, you can't add a reference to a Class Library project to a Silverlight application project. You can only add the reference of another Silverlight application project inside a Silverlight application project.

Silverlight.js is a helper file which enables websites to create advanced Silverlight installation and instantiation experiences. You can call the createObject and createObjectEx functions defined in this file to embed the Silverlight plug-in in a web page.

23. What is XAML?

XAML stands for eXtended Application Markup Language. XAML contains XML that is used to declaratively specify the user interface for Silverlight or WPF applications. For example, if you need to display a rectangle, this is the XAML you need to use:

When the above XAML is executed, it will display a rectangle filled with red color. You may notice that XAML is very similar to HTML in nature.

XAML stands for eXtensible Application Markup Language, and is a declarative markup language that follows the XML rule and is used for developing User Interfaces in WPF and Silverlight technology. XAML files are XML files that generally have the .xaml extension, and separates the UI definition from the run-time logic by using code-behind files, joined to the markup through partial class definitions.

XAML has a set of rules that map object elements into classes or structures, attributes into properties or events, and XML namespaces to CLR namespaces. XAML elements map to Microsoft .NET types as defined in referenced assemblies, and the attributes map to members of those types.

The first element in AppManifest.xaml is a Deployment node. This node defines the application, and contains the child AssemblyPart nodes.

As you can see the AssemblyPart nodes define what assemblies (DLLs) are contained within the .xap file, and give each of them a name.

Now, if you look back up to the top, you'll see the Deployment node has the EntryPointAssembly and EntryPointType attributes. The EntryPointAssembly attribute defines which assembly defined below (as a child AssemblyPart node) is the main assembly (DLL) for the application. And, the EntryPointType attribute specifies the class contained within the assembly (DLL), defined in the EntryPointAssembly attribute, is the main class that will be instantiated to start the application.

The Deployment node also has a RuntimeVersion attribute that defines the version of Silverlight the application is built for.

The .xap file contains an application manifest (AppManifest.xaml) file and all the necessary DLLs that are required by the application. The first DLL contained is the compiled version of your application and has the same name of your application. In my test, I created an application named "SilverlightApplication1", so the DLL is named "SilverlightApplication1.dll". The rest of the DLLs are the dependencies the application requires.

26. What is app.xaml?

App.xaml is a file used by Silverlight applications to declare shared resources like brushes, various style objects, templates etc. Also, the code-behind file of app.xaml.cs is used to handle global application level events like Application_Startup, Application_Exit, and Application_UnhandledException (similar to the Global.asax file for ASP.NET applications).

When Visual Studio creates the app.xaml file automatically, it creates a few event handlers with some default code. You can change the code appropriately.

29. What is MainPage.xaml?

When you create a Silverlight project using Visual Studio, it creates a default XAML file called "MainPage.xaml". This is just a dummy start page created by Visual Studio, and it does not contain any visible UI elements. The default contents of the MainPage.xaml file looks like this:

Deep Zoom provides the ability to interactively view high-resolution images in Silverlight. You can zoom in and out of images rapidly without affecting the performance of your application. Deep Zoom provides smooth in-place zooming and panning.

DeepZoom Composer allows you to create high resolution image compositions which are built for smooth zooming and panning. DeepZoom Composer is absolutely free, and is simple to use - just loads in all your high resolution images and makes your composition on screen.

Deep Zoom Composer is a tool that allows preparing of images for use with the Deep Zoom feature in Silverlight 3.

Silverlight and Windows Presentation Foundation (WPF) are two different products from Microsoft, but have lot of overlap. Silverlight is a subset of WPF in terms of features and functionality.

Silverlight is a Microsoft technology, competing with Adobe's Flash, and is meant for developing rich browser based internet applications.

WPF is a Microsoft technology meant for developing enhanced graphics applications for the desktop platform. In addition, WPF applications can be hosted on web browsers which offer rich graphics features for web applications. Web Browser Applications (WBA) developed on the WPF technology uses XAML to host user interfaces for browser applications. XAML stands for eXtended Application Markup Language, which is a new declarative programming model from Microsoft. XAML files are hosted as discrete files in the Web server, but are downloaded to the browsers and converted to a user interface by the .NET runtime in the client browsers.

Silverlight uses a particular implementation of a XAML parser, with that parser being part of the Silverlight core installation. In some cases, the parsing behavior differs from the parsing behavior in Windows Presentation Foundation (WPF), which also has a particular implementation.

In table format:

Silverlight

WPF

Definition

Silverlight is Microsoft’s latest development platform for building next-generation Web client applications.

Silverlight is generally considered to be a subset of WPF, and is a XAML-based technology that runs within the sandbox of a browser plug-in.

WPF is generally considered to be a subset of .NET Framework, and is a XAML based technology.

GUI

Silverlight will be used in the development of Rich Internet Applications (RIA) for web client users.

WPF will be used in the development of Rich Windows Graphical User Interfaces (GUI) for Windows client users.

Support

Cross OS, cross browser, cross device.

Windows only.

Software Required

Silverlight is the add-on mechanism available for most browsers; in order to run Silverlight applications at client machines, we need to install Silverlight software on the client machine once.

WPF, on the other hand, does not support any plug-in mechanism; instead, we need to install a completed WPF client application in order to use the WPF application at the client place.

Framework support

Silverlight has a very small, its own rich base class library to make the plug-in as small as possible. It is highly optimized for size, and is a small subset of the full .NET Framework, to be embedded within an application.

WPF, on the other hand, has full access to the main .NET Framework and all its associated assemblies.

Deployment

Silverlight applications are hosted within a web server and a web page. To minimize client download size, Silverlight uses a XAP archive. A XAP archive is a zip-compressed archive of the Silverlight application, plus a manifest file describing the content. Visual Studio automatically generates the XAP archive when using the Silverlight project template.

Adobe Flash is the most popular competitor to Silverlight, supporting browser plug-ins and enabling the execution of rich content for the Web. Flash is not a new technology, and already has had a long life span as compared to Silverlight. But it does not have a huge community as expected; it may be because of the limited development tools which are not known to most developers. Flash uses ActionScript as the programming language and Flex as the programming environment, and most developers are far from these technologies.

For ASP.NET developers, to extend their websites using Flash content is not so simple. They need to learn a development environment like ActionScript and Flex. Apart from that, there is no way to generate Flash content using server-side .NET code, which means it’s difficult to integrate ASP.NET content and Flash content.

Silverlight aims to give .NET developers a better option for creating rich web content. Silverlight provides a browser plug-in with many similar features to Flash, but one that’s designed from the ground up for .NET. Silverlight natively supports the C# language, and uses a range of .NET concepts. As a result, developers can write client-side code for Silverlight in the same language they use for server-side code (such as C# and VB), and use many of the same abstractions (including streams, controls, collections, generics, and LINQ).

Microsoft ASP.NET AJAX, a set of JavaScript libraries built into ASP.NET 3.5, is available as a separate download for ASP.NET 2.0. Being an integral part of ASP.NET 3.5 and the AJAX Controls Toolkit for ASP.NET 3.5, now ASP.NET AJAX client-and server-side libraries are more integrated with Visual Studio 2008. The client-side library allows you to implement client-level processing such as processing and validating information entered by the end user, refreshing a portion of the web page, and developing rich, interactive user interfaces. You can also efficiently integrate the client-side library components with the server-side ASP.NET controls library in asynchronous mode. The key technology driver of ASP.NET AJAX is scripting. In general, script-based web applications face several challenges due to different browser settings (e.g., JavaScript is not enabled by default) on PCs and mobile devices. As a result, scripting is often not always the best strategy for enterprises to use to develop secure and scalable RIAs.

ASP.NET AJAX supports limited features of RIAs, and does not support effective multimedia integration, managed code-behind integration, or metadata and information management. Microsoft ASP.NET AJAX is a widely accepted model for building RIAs, but it is very likely that, having Silverlight as an option, .NET developers will migrate ASP.NET AJAX applications to Silverlight RIAs. Visit www.asp.net/ajax/ if you want to learn more about Microsoft ASP.NET AJAX.

There are three different types of Layout controls provided by Silverlight:

Canvas - Position child elements absolutely in x, y space.

StackPanel - Position child elements relative to one another in horizontal or vertical stacks.

Grid - Position child elements in rows and columns.

You have to add a layout panel to every XAML page you create. All other UI elements must be added inside one of the layout panels. Each page can have exactly one layout panel control.

37. Are XAML files compiled or built at runtime?

XAML files are usually compiled rather than parsed at runtime. But it also supports parsing during runtime. When we build a XAML based project, you will see it creates a g.cs extension in the obi\Debug folder. Therefore, for every XAML file, you will find a g.cs file. For instance, a MainPage.XAML will have a MainPage.g.cs file in the obi\Debug folder. In short, at run time, you actually do not see the XAML file. But if you want to do runtime parsing of the XAML file, it also allows that to be done.

By using Expression Studio and Visual Studio, designers and developers can collaborate more effectively using the skills they have today to light up the Web of tomorrow.

By leveraging Silverlight's support for .NET, High Definition video, cost-effective advanced streaming, unparalleled high-resolution interactivity with Deep Zoom technology, and controls, businesses can reach out to new markets across the Web, desktop, and devices.

The answer to this is no - a cross platform version of the .NET Framework is included in the 6 MB Silverlight 4 download, which means you do not need to have anything extra installed on the client in order to access Silverlight applications in the browser.

The Silverlight version of the .NET framework includes the same CLR engine (same GC, type-system, JIT engine) that ships with the full .NET Framework, and a subset of the .NET Framework namespace libraries. You can see the full list of all classes/namespaces that are included by opening up the Object Browser when you create a new Silverlight application using Visual Studio.

RIA stands for Rich Internet Applications, which are Web applications with rich user interfaces including media elements such as audio, video etc. You can think of them as being similar to powerful and rich desktop applications, except that RIA applications are Web based.

Microsoft .NET RIA Services helps to simplify the n-tier application pattern by combining the ASP.NET and Silverlight platforms. RIA Services provides a pattern using which you can write application logic that can run on the mid-tier and controls access to data for queries, changes, and custom operations. It also provides support for data validation, authentication, and roles by integrating with Silverlight components on the client and ASP.NET on the middle tier.

The user interface elements of Silverlight applications are defined in XAML files. The logic and functionality of Silverlight applications is implemented using managed NET code-behind files that share the same class with the XAML file.

Some high-end Windows specific features of WPF, such as real 3D, hardware-based video acceleration, and full document support, will not be supported in Silverlight. This is by design in order to serve Silverlight’s cross-browser, cross-platform reach scenario that demands a light weight plug-in. That being said, Silverlight will offer a uniform runtime that can render identical experiences across browsers on both Mac OS and Windows.

Microsoft designed Silverlight with the ability to deliver high-fidelity experiences on the broadest set of system configurations. Some features, such as HD video, may benefit from the power contained in newer personal computers.

Technically, Silverlight and ASP.NET are completely different. The major differences are listed below:

Silverlight runs completely on the client, while ASP.NET mainly runs on the server, but also has a few parts running on the client.

When an event fires, Silverlight handles the event on the client, but in ASP.NET, the browser will make an HTTP POST to the server, and after the server handles the request, it sends a new HTML page to the client.

A Silverlight application sends rendering commands to the Silverlight rendering engine by either writing XAML or code, and the Silverlight rendering engine will handle the rendering task. On the other hand, ASP.NET doesn’t have a rendering engine. It generates an HTML file on the server, sends it to the client, and allows the browser to parse the HTML file and render the content.

Silverlight can’t work with a database directly; instead, it consumes data from Web Services, while ASP.NET has strong support for working with databases directly.

The most important thing to note is what runs on the client and what runs on the server, since this will affect almost every part of your system. Silverlight runs on the client, and ASP.NET runs on the server. They can work together and are compatible with each other, but this requires some time and effort.

This depends on different scenarios. Below are some common approaches:

Pure Silverlight

One approach is to completely remove ASP.NET. This solution works best if you’re working on a new development. You only need to work on Silverlight, without any worry about integration problems. If you need to communicate with the server, you write Web Services, such as WCF. It will also help you when you need to port part or whole of your system to another hosting or even another platform, since the client and the server are completely separate.

Major ASP.NET, plus a Silverlight island

This approach is generally used when the Silverlight content and the ASP.NET content have little relationship. For example, an ASP.NET blog engine with a Silverlight media player in a blog post. This approach is very easy to implement, and allows you to reach the broadest audience. For example, if a user hasn’t installed Silverlight, he can still read the blog posts, but he can’t watch the videos.

Use ASP.NET AJAX instead of Silverlight

ASP.NET AJAX is designed to work with ASP.NET. It is mainly an extension to ASP.NET. While AJAX can’t provide you the advanced user experience that Silverlight can, for many scenarios, it should be sufficient. This approach also helps if you have strong ASP.NET experience, but are still quite new to Silverlight.

Within this approach, there are two branches. One is to mix the client and server code by using the UpdatePanel, AJAX Control Toolkit, and etc. The other method is to take the pure AJAX approach, where you write HTML and JavaScript instead of using server controls, and call Web Services to communicate with the server. The former branch is easier to implement, especially if you have strong ASP.NET experience but lack JavaScript knowledge. The latter branch proves to be better in an architecture when you want to port an AJAX application to other technologies such as Silverlight, especially since you only need to rewrite the client side code, and can keep the Web Services as they are. The programming model for the latter branch is similar to Silverlight. Therefore, this approach is rarely taken if you’re experienced in Silverlight.

Mix Silverlight with ASP.NET

More often, you may want to port an existing ASP.NET application to Silverlight, but you don’t want to completely rewrite the entire application. This is the most difficult approach since you’re mixing client side and server side technologies.

Before going with this approach, please consider if the above approaches can solve your problem. Ask yourself the following questions:

Do you really need a rich interactive user experience?

This is normally a requirement for consumer oriented applications, but for most business applications, you only need a “good” user experience, which AJAX is sufficient to provide.

Can you add Silverlight islands to your existing ASP.NET application instead of mixing the contents?

This should work for most scenarios. For example, Windows Live Mail is built in ASP.NET, with a few Silverlight islands, such as a slideshow program that allows you to view photo attachments with enhanced experience (actually, most Microsoft created web applications take this approach).

Will this be a good chance to revise your architecture?

Most traditional ASP.NET applications use the B/S or three tire architecture in which the application works with a database either directly or through a business logic layer. When porting applications to other platforms, these architectures will introduce many problems. When investigating Silverlight, it is also a good chance to adopt SOA. Add a service facade layer on top of the business logic layer, and you can work with the services from almost any client, such as an ASP.NET application and a Silverlight application. If you are already on SOA, it should be trivial to port to Silverlight, since you only need to rewrite a client application. With SOA, the ASP.NET AJAX approach and the Silverlight island approach will also be much easier to implement.

If none of the above approaches is suitable, you may have to mix Silverlight content with ASP.NET. When using this approach, keep in mind that Silverlight can’t call ASP.NET server-side event handlers, and each post back (either partial or complete) will cause the Silverlight application to reload.